Traction drive for liquid treating



Oct. 9, 1951 c. H. NORDELL TRACTION DRIVE FOR LIQUID TREATING APPARATUS 2 Sheets-Sheet 1 Original Filed Aug 25, 1941 INVENTOR. BY am" r22 4? Oct. 9, 1951 c. H. NORDELL TRACTION DRIVE FOR LIQUID TREATING APPARATUS 2 Sheets-Sheet 2 Original Filed Aug. 23, 1941 Reissued Oct. 9, 1951 TRACTION DRIVE FOR LIQUID TREATING APPARATUS- Carl H. Nordell, Palm Springs, Califi, assignor to Infilco Incorporated, a corporation of Delaware Original No.

2,418,189, dated April 1, 1947, Serial No. 408,115, August 23, 1941. Application for reissue November 28, 1947, Serial No. 788,332

(Cl. 210-55) Matter enclosed in heavy brackets appears in the original patent but forms no part of this 17 Claims.

reissue specification;

This invention has to do with the separation of liquids and solids and the general purpose is to of the liquid or to secure the solids in more concentrated form for use or disposal.

This invention has more particularly to do with the handling of the solids that deposit at the bottom of such apparatus and is directed to providing improved means for moving such solids to an outlet.

When the amount of liquid to be handled is small it may be passed through a small chamber having a sharply sloping bottom on which the deposited solids will slide to an outlet. Such apparatus is commonly spoken of as a settling tank. When the amount of liquid to be handled is large or the solids separate so slowly that a long retention time is necessary, then the tank or basin must be cfcorresponding size or volume and experience has shown that it is better to obtain the necessary size or volume by increased area rather than depth. Such basins may be round or rectangular and are frequently 100 feet in diameter, some being much larger. In such size it is not practical to use a bottom of sufiicient slope because of the depth and cost involved and for other reasons. Consequently, it is the usua1 practice to provide a slightly sloping bottom and a scraping mechanism to move the solids to an outlet. While in rectangular basins the scraper may be of the drag type, moving in straight lines across the floor, in circular basins and in some rectangular basins the scraper revolves about a center in the basin.

Because it is simpler so to do and more readily understood, I will for purposes of exemplification describe my invention in connection with a clarifier having a basin of circular form although the principle thereof can be applied and utilized in basins of other form.

In general, such a clarifier will comprise a basin of suitable diameter and depth according to the quantity and character of the liquid to be treated. In the bottom of the basin and adjacent the floor will be a scraper mechanism and there will be provided suitable means to support this scraper and to slowly rotate it. In the fioor of the bsin, usually adjacent the center, is a sludge matter printed in italics indicates the additions made by reissue.

outlet and the blades of the scraper are pitched to move the solids toward this outlet. The basin will have an inlet for the raw liquid, in a circular basin this is usually at the center, and there will be an outlet at the top which is commonly in the formof alaunder having an inner weir edge and a suitable discharge. Many forms of scraper mechanism and of the support and the driving meansthereforhave been proposed and are in This invention has to do primarily with the driving means'but comprisesalso certain modifictions oftheiscraper mechanism or its support andmeansoi attachment or cooperation between the scraper and the drive. One: object of my'invention is to make the drive more positive.

. Another object is to protect certain parts of the drive mechanism from interference by or because of weather conditions and so receive proper operation. H v

Another object is to utilize the resistance to motion of the scraper mechanism, as by the inertiaor friction of the material to be moved, to increase the traction effect.

Another object is to provide a connection between the scraper and the drive such that increased resistance to the former will aid the latter in overcomingsuch resistances.

A principal object is toprovide a form of drive or driving mechanism tht may be used in clariiiers of any size.

Another object is to improve the operation of such apparatus by an improved drive that is more positive and certain under adverse conditions of load andweather.

Other objects will be mentioned specifically hereafter or will become apparent upon consideration of the accompanying disclosure.

Clarifiersof the sort under consideration may have a centrally positioned column, which carries a major part of the weight of the scraper and other mechanism. In some cases the drive mechanism comprising a prime mover and reduction gear is mounted on this column. This form has advantages where the required torque is small but is not well adapted to cases where the deposit is heavy or otherwise hard to move or where the clarifier is of considerable size requiring correspondingly heavy gearing and other parts.

In the past many clarifiers have been built with a track around the periphery, this track being mounted on the top of the clarifier walls sirable forms of structure.

the weight of the scraper mechanism and thus as the carriage is slowly driven around the track the scraper is su ita'blyrotated. This type of drive has many advantages but in practice certain difficulties are encountered. Thus, in winter, ice will form on the track or wheels or at any time grease may get on the track, with. .the result that there is insuflicient friction for travel to continue. It is also common during a heavy sleet or snow storm to have such a considerable building up of snow or ice that the power available to drive the carriage is :not suflicient even with traction, and the carriagestops. Proteetive shields or coverings over the track have "not proven sufficient since these must be at least partly open and as the track must extend 360 around the "basin snow and sleet will drive in somewhere, besides'which such protection is relatively expensive. So common is trouble from such sources that it is common to install some sort of signal device that will operate when the carriage comes to a stop, While helpful such devices do .not meet the situation because frequently clarifiers are used in a service where there is no attendant available during long periods. Also, it may not be practical to keep the track clear. During such periods of cessation solids continue to accumulate and may do so to such an extent that clarification is not obtained or that the scraperv cannot be moved when the original cause of stoppage is overcome. In any .case proper operation of the :plant of which the clarifier is a part.is.seriously-interfered with or ceases.

Since the major part :of :such trouble arises from bad weather conditions I'propose-to put the track in a place where it is not reached by the weather and to dothis by-the simple and inexpen- -sive expedientof submerging the track in the liquid in the apparatus. The track may be near the surfaceor-maybe lower down as preference or special 'consideration"may dictate. The important thing is'that'the'liquid in the apparatus protect the track. If desired the 'bottom of the tank itself may be used as a track.

In thus submerg'ing -the track 'I submerge also, at least in part, the wheel .or wheels that rest .uponorcooperate with the track. If fully submerged no .ice will adhere to the wheels. partially submerged they may be protected .by a

guard or the little iee thatdoes adhere to the wheel can be readily scraped off. It is to be understood that the :wheel will rotate once or twice a minute depending on thediameterchosen, during which period-little ice or snow will adhere even if exposed, 'whereas the travelaround the track is slow, at arate of about .5 feet a minute so that a complete :circuit will take. from about 15 .minutesin a very small size to an.hour or even more in larger sizes, during which time .much more snow or-ice cancollect.

In the past it has been necessary to put a very considerable load on the carriage in order to' receive the required tractive effect and this has at times requiredadditional structure and unde- I now propose an apparatus wherein 'the "construction ,of the scraper itself and of the other associated parts may be designed without regard forsuch carriage .loading and the necessaryfriction for traction ,obtainediby otherrneans, as will beLhereafter described.

.mounted .ona turntable, 26,

Figures 1 and 2 taken on line 33 of Figure 1.

Figure 4 shows a modification of the mechanism of Figure 3.

Figure 5 is-an elevation of another form of drive.

A clarifier, with which my invention is associated, as shown in Figures 1 and 2, comprises a .basin, H, which v:may be of any desired shape,

such as square or rectangular, or circular as shown in'the drawing. The basin, H, is formed by a suitable vertical .wall, '12. and ahorizontal .Wall or floor, 13, At the top tof the Wall, 42, a weir, [4, permits the overflow of liquid into a launder, :5, which is connected to a discharge conduit, 1.6. Preferably, the floor, willslope a ually to a slud e sump. I-' wh nthe ca e of a circular basin, wouldprobably be adjacent the center. A sludge withdrawal line, 31:8, runs frcm the sump, II, to a suitable point of discharge, not shown.

It is customary in the construction ofa circular clarifier to provide for .the discharge of .raw liquid into the center of thetank, and toprovide a rotatable scraper means for pushing settled solids to the sludge sump. :With a rectangular basin the influent-conduit ordinarily discharges at one end of the basin while the ,eflluent line leads from the vopposite end, and any suitable means may be used to scrape settled solids .to'a

sludge sump, which maybe located at either end or in the middle. For the purpose of illustrating .my invention I have shown a'circular-basin. At

: Walkway to the mechanism located'on [the pillar.

InFigures l and.2,.I show a central column, 1.9, rising from the center of thefioor, I3, .toa height well above the water level fixed by .the weir, 14.

Preferably, the column, vl9, will contain the infiuent conduit, 20, .which preferably. discharges, as'at 2|, intoaloading-well, 22,.or othersuitable bafiie means adapted to direct:the fiowtof raw liquid downwardly. The :loading well may be constructed of any suitable material, such .as metal or wood, and may-comprise an open-cylinder supported "either by the pillar or by the scraper truss. Obviously, such a loading :well should extend well above the.=liquidslevel, .I :4,,;in the basin, II, and shouldalso'extend to apoint below theinlets,.2 I, sothat liquid will havestofiow downwardly in the .centerof the-tank and may thereafter have a quiescent .flow toward .the efiiuent weir, H.

A rotatable scraper truss, ;23, is .mounted in the basin, H. .The truss is provided with a plurality ofscraper.blades,. 24, set to movesolids inwardly duringitsoperation to the sludge sump, IT. The scraper-truss, Z3, is,suspended.in.any suitable fashion, as by..truss.supportmembers, .25, and rotates on a suitable bearing-or .aturntable support, 21, on the top of thepillar'lll. In the drawing, the loadfact with the lower edge thereof.

ing well, 22, is shown mounted on the scraper truss, 23, and rotatable therewith.

It is often necessary for an operator to have access to the turntable and adjacent parts so that it is customary to provide a bridge or walkway, 28, running from the periphery of the tank to the center pillar. In many installations, the scraper truss, 23, and the bridge, 28, are rigidly secured to each other so that both rotate at the same time. In other installations the bridge may be fixed and the scraper truss rotate independently thereof. I prefer the former type of construction although my preferred form does not take the form customarily used. Ordinarily, the bridge and truss are rigidly secured to each other at the center so that rotation of the bridge causes rotation of the truss. Obviously, this results in considerable stress at the central connection and requires heavy construction at that point. I prefer to pull the truss along the basin wall from its periphery, thus avoiding the great torque stress developing in the center in the ordinary construction.

For the purpose of my invention, I prefer that the inner end of the walkway, 28, be rotatably mounted on the pillar, l9, and that the other end he supported by an integral carriage, 29, which rides upon an annular track or rail, 39, mounted on the inner side of the wall, I2, by any suitable means, such as brackets, 3|. customarily, and as shown in the drawings, the walkway, 28, and the carriage, 29, cooperate and are joined to form a unitary structure, so that it could be said that the carriage is part of the walkway,-or vice versa. In Figure 2 I have shown the track, 39, as mounted away from the wall, l2, of the tank. However, it will be understood that such a track may be embedded in, as well as supported by, any wall, including the floor, or may even be such a wall itself. It will also be understood that such a track may be suitable for supporting weight or furnishing traction, or both. In this specification, and in the claims which follow, the word track is used in its broad sense to include any tank wall or any rail or track mounted thereon. The track should be sufficiently below the surface of the liquid to prevent coating by ice, it being understood that in such basins the water must be warm enough to avoid freezing as operation of a clarifier is impossible if ice should form along the weir, l4. The carriage, 29, may be constructed in a great variety of forms but for purposes of illustration I have shown preferred embodiments in Figures 3 and 4. In Figure 3, the carriage comprises a plate or frame, 32, in which is journaled a rotatable shaft, 33, on which is rigidly mounted a wheel, 34, riding upon the upper surface of the rail, 30. In many cases rotation of the wheel, 34, will be sufficient to rotate the walkway, 28, and the scraper mechanism which includes the truss, 23, and the blades, 24. When the friction required to effect this result can be secured I contemplate my invention in this form. In such a case as this it may be found simpler and otherwise desirable not to rest the drive wheel, 34, on the track, 39, but to omit this track and let the drive wheel rest upon, and secure traction from, the floor, l3, of the basin, as illustrated in Figure 5 and described more fully hereafter.

When the force required for rotation of the scraper mechanism is greater than can be secured by such a simple construction, I may mount a second wheel, 35, below the rail, .30, and in con- The lower wheel, 35, can be mounted in any suitable manner, such as on a shaft, 35.

The peripheral end of the walkway, 28, in my preferred form, is supported above the carriage, 29, in any convenient manner, such as by risers, 31 and 38. I prefer to place the driving motor, 39, upon a lateral extension of the walkway, 29, which, as above stated, is supported by the carriage, 29. The motor, 39, may be supplied with current by any suitable means and as such means are well known and in themselves are not part of this invention they are omitted for sake of simplicity. A speed reducer, 40, is connected to the motor, 39, is driven by it, and in turn drivesa shaft, 4|. A sprocket, 42, rigidly mounted on this shaft, 4|, is connected by a chain, 43, to a sprocket, 44, which is rigidly mounted on the shaft,'33, carrying the upper wheel, 34. In this manner, when the motor, 39, is operating, the upper wheel, 34, is driven at a desired speed on the rail, 30. When two wheels are necessary, I prefer that both be driven by the motor, 39, and. in such a construction I provide a sprocket, 45, mounted on the shaft, 36, to drive the lower wheel, 35, and connect it by a chain, 46, to a sprocket, 41, likewise driven by the reducer, 40

so that operation of the motor will drive both sprockets, 44 and 45, and consequently both wheels, 34 and 35.

I attach two arms, 49 and 49, from the front and back end of the carriage frame, 32, and join them adjacent their lower ends, such as at 50. The lower end of one such arm, as at 5|, is connected to a trailing link, 52, which is also joined in some suitable way to a pin, 53, extending from the lower portion of the truss, 23, and upon which revolves a wheel, 54. It will be obvious that as material collects upon the floor and requires greater force to push it to the sludge sump, I1, pull on the trailing link, 52, will pull on the arm, 48 and 49, which will tend to rotate the carriage, 29, on a horizontal axis and so will cause both wheels, 34 and 35, to press more firmly against the rail, 30. This rotational effect on the carriage will increase the friction between the wheels proportional to the resistance of, i. e., the workv to be done by, the scrapers, 24.

In some cases, as for instance where the load is very heavy or the liquid contains grease or greasy material, itmay be desirable to provide a more direct and powerful drive than can be had by friction alone. This is contemplated and a suitable apparatus is shown in Figure 4. In this form, the general construction of the basin, truss, scrapers, center column, walkway and motor drive may be as illustrated in the other figures so that a description of those parts is not necessary. As shown in this figure, the weight of the carriage and walkway is borne by two wheels, and GI, rotatably mounted upon shafts, 62 and 63, suitably journaled in a carriage frame, 64. The walkway, 28, is supported above the carriage by risers, such as 65 and 66. In this embodiment, the rail, 30, is modified to provide a rack, 61, on its lower edge. Meshing with the rack, 61, is a pinion, 68, mounted on a shaft, 69, journaled in the carriage frame, 64. The sprocket, 42, of the speed reducer, 4|], is connected to a similar sprocket, 10,

(tithe pinion to revolve when the sprockets are 7 driven :by :the i'motor, ,39. The carriage frame, 64, is connected to the peripheral .-=end :of the truss, 23, by any suitable means, suchas :links. 1-2 and 13. ;It will beobvious that in this embndiment the operation of the motor, :39, will rotate the pinion, '58, which will furnish suitable positive force to :drive thecarriagealong .the rail, 30, even against zgreat resistance.

A further embodiment .of .my invention is shown in Figure 5. In this form the :generaliconstruction of the basin, .scraper, truss and wall-:- way, :motor and similar elements, .is :thesame as that :shown in the other ifigures and need .not be repeated. In this embodiment, the scraper :truss, 23,;isprovided with a wheel or wheels which .rest upon the floor, 13, of the tank, which wheels are driven'byany suitable means from the motor, '38. aIn'ithe drawing .1 show two wheels, 89. and .81.,

mounted at .the peripheral .end of the truss, '23.-

fIlhecircum'ferential end of the walkway, '28, and the truss, 23, are connected by suitable strut members, 8 2 and .83, .therebysupportingrthe outer end :of :the walkway. One of the wheels, such as, 81, "is'provided with a sprocket, J84, which is connected .by :a chain, 85, with-the sprocket, M2,

of the speed reducer. In this embodiment the operation of the motor drives :the wheel, 81, which causes the rotation .of the truss (and scraper around the basin.

As the operation of such a clarifier .is thought to be obvious it will be only briefly described. The liquid enters through the conduit, "2t, and escapes through ,the openings, 21, into the load-- ing 'well, '22, which aids in distribution of :the :liquid. During the periodof slow flow across to the periphery of the tank solids deposit :and the clarified liquid escapes over the weir, it, into the launder, I 5,:and so to the-outlet, I 6. As the carriage, 29, is moved along the-trackasdescribed, it rotates the outer or circumferential end of the walkway, 28, and the truss, 23, which carries the scrapers, '24, which moves solids along the floor to the outlet, I 7. I do not elaim such a clarifier as a whole nor the general relation or operation of parts thereof. My'invention has to do only with the driving mechanism, and with the way and place a portion of the load is-car ried and utilized.

It will be obvious to those skilled in the art that many modifications and variations of the invention hereinabove .set :forth can be made. "For example, it is possible that there be no connectionbetween the walkway, 28, and the truss, 2*3, 'at their peripheralends, as shown'inthe figures. in this event the circumferential end of "the walkway will :be driven by the .meansshown'and the center of the walkway and the :truss so se- .curedtoeachotherthat the'rotation of the Walk- :way will causerotation of the truss. 'Whilesuch ca :construction is more cumbersome, due toit-he agreaterstressestarising in such a form of appazratus, it is contemplated as included within my ,invention. ;It .would also be possible :to utilize my invention in a rectangular clarifier, in which -event;the trusscould-besupported at each end on rails spaced from the sides of the tank, whereby the'scraper-means:couldibe :driven back and forth :trom ;one .end of the tank to the :other. This .form, also, is manifestly contemplated as in- :cluded within my invention. It will be obvious also that the word traction is used "herein in .its broad :sense to include any cooperation she- :tween a moving wheel and .a fixed surface Ito :cause movement of the carriage or :scraper, whether this is by :pushing or by pulling. An-- cordingly, the appended claims are to be given an interpretation commensurate with the novelty herein described and as broad as may be permitted by prior art.

I claim: I

1. Ina liquidand solids separator comprising a tank having an inlet for liquid to be treated, an overflow weir 'for the escape of clarified liquid, an outlet for separated solids, and aisolids scraper adapted to move separated solids :over the bottom :of .said tank toward said solids :outlet, :an improved means for operating said solids scraper comprising a carriage, a fixed traction surface in said tank at a level below the level of said weir, a traction -Wheel carried by said carriage, engaging said traction *surface-and-traveling along the same, amotor supported by said carriage, a power transmission mechanism joining said motor to said wheel, and'a connection joining said carriage to saidscraper.

.2. "In combination with a liquid treating apparatus comprising a tank having an .inletjor liquid to be treated, an overflow weir for the escape of clarified liquid, an outlet for separated solids, and a ,member rotatable about a vertical axis for 'movingsolids across the ,fioorof the tank, a means for rotating said "member comprising a carriage, a stationary track in said tank below the level of said weir, :a traction wheel carried by said carriage and engaging said track, :a motor supported by said carriage, a power transmission mechanism joining-said motor to said wheel, and a connection joiningsaid carriage to-said rotatable member. 7

3. In a liquid and solids separator comprising a tank having an inlet for liquid to be treated, an overflow weir for the escape-of clarified liquid,

, an outlet for settled solids, and :a solids scraper operable to move materialacross the bottom of said tank, an improved :means for operating @said solids scrapercomprising a stationary track having a traction surface within'said tank and below the level of saidweir, a carriage connected to saidsolids scraper, a traction wheel (carried by said carriage :and engaging said traction surface, .a motor supported by said carriage, :and .a power transmission mechanism joining said modzor :to said traction wheel.

4. Theapparatusof claim 3 wherein the traok :com'prises arack and the traction wheel is in the form of a pinion meshing with said rank.

-5. The apparatus-of claim 3 whereinthe track is-mounted on -a vertical :wall of :said tank.

6. The apparatus of ,claim 3 whereinthe traok :is-an .annularpath on the floor of the tank.

*7. ma liquid and "solids separator comprising acircular tank, an inlet for liquid .to be treated opening into said tank, an :outlet 'for clarified liquid leading .from the upper portion of said tank and an outlet forsedimented solids adjaccent=the floor of said tank, a central pillar :within said tank, and a solids scraperoperating overthe bottom of said tank and rotatable around and at least partiallysupportedby said central pillar .and so constructed and arranged as to move solids depositing upon the :floor of said tank -:to .said solids outlet, :an improved means for rotating said solidsscraper and for supporting theper- .ripheral end of 'such scraper comprising a stationary track within said tank and having a sun.-

sface'below'the level of saidoutlet, andatraction wheel engaging saidisurface,arconnection joining said wheel to said scraper, and :means for retatingsaizd traction wheel.

18. .Inzafliquid and solids separator comprising ,uid from the upper portion of said tank and establishing the normal liquid level in said tank,

a central pillar within said tank, a solids outlet from the bottom of said tank, and a solids scraper adapted to operate over the bottom of said tank and rotatable around and at least partially supported by said central pillar, an improved 'means for rotating said solids scraper comprising' .a stationary track within said tank, said track being provided with a rack below the level of said outlet for treated liquid, a carriage, a gear mounted in said carriage and meshable with said rack, a motor supported by said carriage, a power transmission mechanism operatively joining said motor to said gear, and a connection joining said carriage with said solids scraper.

9. In a liquid and solids separator comprising a circular tank, an inlet for liquid to be treatedopening into said tank, an outlet for treated liquid from the upper portion of said tank, a

solids outlet adjacent the bottom of said tank,

a central pillar within said tank, and a solids scraper operable over the bottom of said tank and rotatable around and at least partially supported by said central pillar, an improved means for rotating said solids scraper comprising a traction wheel mounted on said solids scraper and engaging the floor of said tank, and means for rotating said traction wheel comprising a motor supported by said scraper above the level of said outlet for treated liquid and a power transmitting mechanism operatively joining said motor to said traction wheel.

10. In a liquid and solids separator comprising a circular tank, an inlet for liquid to be treated opening into said tank, an overflow weir for escape of clarified liquid, a solids outlet from the floor of said tank, a central pillar within said tank, and a solids scraper assembly rotatable over the floor of said tank and operable to push solids depositing on the floor of said tank to said solids outlet, the inner end of said assembly being rotatably mounted upon said central pillar, an improved means for rotating, and for supporting the peripheral end of, said assembly comprising a stationary track having a surface within said tank below the level of said weir, a traction wheel mounted adjacent the peripheral end of said assembly and contacting said surface, and means for rotating said wheel comprising a motor and a power transmitting mechanism operatively joining said motorlto said traction wheel.

11. In a liquid and solids separator comprising a tank having an inlet for liquid to be treated, an overflow weir for the escape of clarified liquid, an outlet for separated solids and a solids scraping mechanism for moving separated solids to said solids outlet, an improved means for operating said solids scraper comprising a track having an upper and a lower wheel engaging surface, at least one of said surfaces being below the level of said weir, a carriage, a first wheel mounted on said carriage and engaging one of said surfaces, a second wheel mounted on said carriage and engaging the other of said surfaces, at least one of said wheels being a traction wheel, the surface engaged by said traction wheel being below the level of said weir and the axes of said wheels being in horizontally separated planes, a motor mounted on said carriage, a power transmission mechanism joining said motor to said traction wheel and a rigid vertically extending member joining said carriage to said scraper.

12. In a clarifier apparatus of the type wherein a liquid and solids are separated including a carriage and operatively connected to said traction wheel, a lever rigidly mounted on said frame, and a link connecting said lever to said scraper mechanism, whereby on the one hand the traction wheel and surface-are protected against inclement weather conditions and on the other the traction effect may be proportioned to theload on the scraper. I

13. In a liquid and solids-separator comprising a tank having an inlet for liquid to be treated, an overflow for the escape of clarified liquid, an outlet for separated solids, and a solids scraper assembly, the combination with said solids scraper assembly of a carriage, a wheel supporting said carriage, a wheel supporting surface supporting said wheel, a motor supported by said carriage, a stationary traction surface in said tank below the level of said overflow, a traction wheel supported by said carriage, the periphery of said traction wheel engaging said stationary traction surface, a power transmission mechanism operatively joining said motor to said traction wheel, and means for pressing said traction wheel against said surface, said means comprising a lever member joined to said carriage and'piv'otable about a center other than the axis of .said traction wheel, and a loading means joined to said lever member in a manner to cause torque in the direction of moving said traction wheel toward said traction surface.

14. In a liquid and solids separator comprising a tank having an inlet for liquid to be treated, an overflow for the escape of clarified liquid and an outlet for separated solids, and a solids scraper mechanism for moving separated solids to said solids outlet, the combination with said solids scraper of a carriage, a wheel supporting said carriage, a wheel supporting surface supporting said wheel, a motor supported by said carriage, a fixed traction surface in said tank below the level of said overflow, a traction wheel supported by said carriage, the periphery of said traction wheel engaging said fixed traction surface, a power transmission mechanism operativ'ely joining said motor to said traction wheel, whereby motive power is transmitted from the former to the latter, and means for increasing the tractive power of said traction wheel by pressing it against the traction surface, said means comprising a loading member and a lever joining said traction wheel to said loading member, said lever and said loading member being so constructed and arranged as to move said traction wheel toward the traction surface.

.an outlet of sedimented solids adjacent the floor of said tank, a central pillar within said tank, a solids scraper operating over the floor of said tank and rotatable around and at least partially prising a fixed traction surface 'in said tank at a v5 leve'l below said outletfor clarified liquid, a carflage, atraction-wheel carried by said carriage, engaging said traction surface and traveling along the same, a motor supported "by said carsiege, 3. power transmission mechanism joining said motor to said wheel and a connection joining said carriage to said scraper.

'16. In apparatus for the treatment of liquid wtthpreeipitation of solids, a tank having awall associated therewith, which wall presents a submergible and normally submerged driveway in thetank; liguidinlet and outlet means associated with the tank, whereby a liquid'ievei can be substantially maintained in the tank, above said driveway; a rramestructure adapted to be moved along said driveway; means to support said frame structure while allowing it to be moved; solids impeller means in the tank, mounted on said frame structure; a drivewheel mounted on the frame structure and adapted to contact said :driveway in a direction normal to said driveway and to the periphery of said drivewheel, with saflicientjpressure to provide traction; and motor' means mounted on said frame structure to drive said drivewheel and thereby to drive said frame structure and solids impeller means. I

17. Apparatus according to claim .16 wherein said "tank is substantially circular, said wall is substantially peripherally located, said liquid pu'tlet means, driveway and drivewheel are 10- cated substantially at the top of the tank, and said liquid inlet means is located remotely from 'said liquid outlet means, whereby saiddrivewheel is'protected from adverse effects of the climate and of the solids precipitated in the tank.

CARL 1-1. NORDELL.

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